Abstract
Few mode optical fibers are a promising way to continue increasing the data rate in optical communications. However, an efficient method to launch and extract separately each mode is essential. The design of a interferometric spatial mode (de)multiplexer for few mode optical fibers is presented. It is based on a single Michelson-like interferometer which consists of standard optical elements and has a reflective image inverter in one arm. Particular care has been taken in its design so that both polarizations behave the same. Moreover, this interferometer can process several pairs of modes simultaneously. The multiplexer also consists of: a phase plate, focusing optics at both ports of the interferometer and elliptical core fibers to recirculate some outputs. It can multiplex ten spatial and polarization modes and it presents low losses and no intrinsic crosstalk between modes. Additionally, it is polarization insensitive, achromatic, compact and inexpensive. The same system can work as a demultiplexer when used in reverse. In this case, both the losses and the crosstalk remain very low. Similar designs that perform other functions, like an add-drop mode multiplexing, are also suggested.
Highlights
The use of optical fibers with a core having a few spatial propagation modes is a promising possibility of spatial division-multiplexing (SDM) to increase the transmission information rate of optical communications in order to meet future traffic demands [1,2]
The interferometers using two Dove prisms [12] or those based on image inversion with spherical lenses can not multiplex several pair of modes simultaneously, because the emerging beams are parallel only if the input fiber is on the optical axis
Note that since only one reflection occurs in each arm, the interferometer is already polarization insensitive, so the Fresnel retarder is unnecessary in this case
Summary
The use of optical fibers with a core having a few spatial propagation modes is a promising possibility of spatial division-multiplexing (SDM) to increase the transmission information rate of optical communications in order to meet future traffic demands [1,2]. Multiplexing can be carried out in multiple ways, for instance by beam-splitters [7], Bragg gratings [8], directional couplers [9], photonic lanterns [10], multiplane light converters [11], or Mach-Zehnder interferometers (MZI) including Dove prisms to rotate the modes [12], a mirror image inverter [13], a refractive inverter [14] or a refractive Gouy’s phase retarder [15]
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